CD33 is a 67 kDa plasma membrane protein that binds to sialic acid and is a member of the sialic acid-binding Ig-related lectin (SIGLEC) family of proteins. CD33 is known to be expressed on myeloid cells. CD33 expression has also been reported on a number of malignant cells. Although CD33 has been targeted for treatment of cancer, e.g., acute myeloid leukemia, no effective CD33-targeted treatments are currently on the market. The present invention solves these and other problems.